220 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1939 



which are fired from it. The immediate problem thus resolves itself 

 into a determination of whether the microscopic markings on the 

 questioned bullet or shell coincide with similar markings upon test 

 specimens fired by the examining expert from the suspected gun. 



To meet this problem, which demands enlargement of the charac- 

 teristic markings and provision for directly observing the coincidence 

 or lack of coincidence between the sequence of the marks, the crime- 

 detection laboratory has drawn upon the field of applied optics in 

 creating an ingenious device known as the comparison microscope. 

 This instrument not only furnishes the required magnification to 

 make the minute markings distinctly visible, but in addition optically 

 "splits" the specimens being compared in such a manner that images 

 of opposite halves of the specimens are placed in proper juxtaposition 

 to permit direct comparison of the marking sequence. In plate 3 is 

 shown a photograph illustrating the manner in which the character- 

 istic markings are seen to flow smoothly from one bullet into the 

 other when both have been fired from the same weapon. 



To illustrate the extreme value of this type of examination, atten- 

 tion is invited to a case in which a trapper in Alaska was found mur- 

 dered in his cabin. Two suspects were located, each of whom w^as 

 in the possession of a rifle of the type from which the fatal bullet 

 had come. However, suspicion was directed more strongly toward 

 one suspect than the other because of a prior criminal record which 

 he was found to have and further because of the presence of blood- 

 stains on his clothing. Upon receipt of the two suspected weapons 

 in the technical laboratory of the Federal Bureau of Investigation, 

 test specimens were fired from each and by means of the comparison 

 microscope were compared with the fatal bullet. When this exam- 

 ination had been completed, it was found that the fatal bullet had 

 been fired from the weapon belonging to the suspect toward whom 

 the finger of suspicion had pointed less strongly, thereby completely 

 exonerating the suspect with the prior criminal record. The blood- 

 stains appearing upon the latter's clothing were found not to be of 

 human origin, the suspect having previously claimed that they were 

 caused by reindeer blood. Thus, it will be seen that the examination 

 not only assisted very materially in the solution of the case, but even 

 refuted circumstantial evidence tending to point to another suspect. 



It is also of importance to note that the comparison microscope 

 is not by any means limited in its application to the examination of 

 firearms evidence. Whenever two objects of differing hardness are 

 forcibly placed in contact, markings characteristic of the surface 

 imperfections of one are invariably impressed upon the other. For 

 example, a pair of bolt clippers used by a burglar to gain access 

 to a business establishment may readily be identified as the instru- 



